Gettext is an internationalization (i18n) and localization (l10n) library for Elixir applications. It provides macros for marking strings in source code that need translation, extracts these strings into POT (Portable Object Template) files, and merges them with PO (Portable Object) files for different locales. At runtime, it looks up translations based on the current locale and supports features like pluralization, context-based translations, domain-specific messages, and string interpolation with compile-time optimization. The architecture follows a library pattern with clear separation between the API (Gettext module), backend behavior (Gettext.Backend), compilation (Gettext.Compiler), extraction (Gettext.Extractor), merging (Gettext.Merger), and specialized components for interpolation, pluralization, and fuzzy matching.